The present invention relates to an infrared thermometer, and, more particularly, to an infrared medical thermometer that receives infrared emission from the tympanic membrane via a narrow fiber optic cable with a radially varying index of refraction , thereby measuring core body temperature.
The core body temperature of a person or of a warm blooded animal reflects the state of his, her, or its health. Fevers of 1.degree. C.-2.degree. C. above normal are the body's normal response to infection. Higher temperatures, as in heat stroke or severe infection, can be rapidly fatal. Thus, measurement of core body temperature is an important medical diagnostic tool, particularly with patients, such as animals and young children, who cannot describe their symptoms verbally. The tragic consequences of misdiagnosing potentially fatal human diseases are obvious. Ignorance of dangerously elevated temperatures in valuable animals may have severe economic consequences, for example if the animals are race horses which have not been acclimated to hot and humid climates.
The classical way to measure core body temperature is by using a rectal thermometer. This requires more cooperation from the patient than often may be forthcoming. Some adult humans and many animals may regard the insertion of a foreign body in their rectums as an invasion of their privacy. In a clinic or hospital setting, routine use of a rectal thermometer invites the risk of transferring infectious body fluids among the patients if proper hygienic precautions are not taken. Thus, it would be highly advantageous to have a non-contact method of measuring core body temperature.
More localized temperature measurements may be diagnostic of localized infections, particularly infections of the middle ear. It is important to know which, if either, of a patient's two ears is infected, particularly if the therapy is to include myringotomy, which includes piercing the tympanic membrane and draining the fluid from the middle ear. Being able to clearly distinguish which of a patient's two tympanic membranes is hotter would make this diagnosis much easier, especially if the patient is too young to describe his or her symptoms verbally.
One promising non-contact method of measuring temperature is infrared thermometry. All material bodies emit electromagnetic radiation. The emission spectrum is described by Planck's law. Bodies at temperatures near ordinary room temperature have emission spectra that peak in the mid-infrared, at wavelengths around 10 microns. By the Stefan-Boltzmann law, the intensity of emission is proportional to the fourth power of the temperature. Thus, the temperature of an object can be measured by measuring its infrared emission, using any one of many sensors known to the art, such as thermopiles, pyroelectric sensors, bolometers, or active infrared sensors. Several such devices have been patented, for example, by Fraden (U.S. Pat. No. 5,368,038), Seacord et al. (U.S. Pat. No. 5,167,235), and Pompei (U.S. Pat. No. 5,445,158). These three patents are incorporated by reference for our purposes as if fully set forth herein. In these devices, infrared radiation from both the tympanic membrane and the walls of the ear canal are transmitted by a waveguide to an infrared sensor. These devices provide means for convenient non-contact body temperature measurement. However, they sense infrared radiation emitted both by the tympanic membrane and by the generally cooler ear canal. Therefore, they do not measure the true core body temperature, and do not have sufficient resolution to distinguish infected ears from uninfected ears. Pompei recognizes this problem, and advocates scanning the tympanic membrane, on the unverifiable assumption that the highest temperature thus measured is the true core body temperature.
There is thus a widely recognized need for, and it would be highly advantageous to have, a medical thermometer capable of non-contact measurement of core body temperature via measurement of tympanic membrane temperature alone, without interference by infrared emissions from the surrounding ear canal.